During embryogenesis, numerous morphological events appear to require the involvement of the extracellular matrix to proceed normally. These cell-substrate interactions which influence tissue organization through cell adhesion and migration, are mediated, in part, by the transmembrane heterodimeric ab receptors termed integrins. Using specific commercially available antibodies and peroxidase immunocytochemistry on frozen sections, we have localized a1b1, which recognizes laminin and several collagens, a5b1, a fibronectin receptor, and a6b1 which binds exclusively to laminin, during blood vessel formation and somitogenesis in early macaque embryos (stages 11-16). Our results show selective expression of the integrins in this crucial developmental period, indicating differing morphogenetic roles for each receptor. During angiogenesis, a1b1 and a5b1 expression on endothelial cells of more developed vessels, indicates they may perform a stabilizing function by anchoring endothelial cells to the underlying basement membrane components. A5b1 may also facilitate cell adhesion and migration along fibronectin pathways by appearing on angioblasts at the onset of vasculogenesis. The a6b1 integrin, while apparently not directly associated with angiogenesis, appears involved with somite differentiation, being present on mesenchymal core cells within the myocele of epithelioid somites, and also on presumptive sclerotome cells with the commencement of differentiation. The expression of a6b1 on myotome cells in latter stages is consistent with its proposed role in myoblast formation and migration. Some of these findings differ from those described in other studies, and therefore, may represent important variations in the expression and subsequent function of these integrins between species.